Radiotelephone credit card data communications

ABSTRACT

Method and apparatus for communicating credit card information read at a mobile radiotelephone unit is disclosed. Data read from a credit card is placed in a variable length error protected format and transmitted from the mobile radiotelephone unit to authorize payment of the radiotelephone call.

BACKGROUND OF THE INVENTION

This invention relates generally to radiotelephone systems and equipmentand more particularly to the method and apparatus used to communicatecredit card information in a radiotelephone system in which a creditcard is used to prepay for the radiotelephone call. This invention isrelated to U.S. patent application Nos. 057,402 (D'Avello et al.) and057,479 (D'Avello et al.), each filed on the same date as the presentinvention and containing related subject matter.

Widespread mobile telephone service such as that afforded by cellularmobile telephone systems enables large numbers of users to haveradiotelephone service in their vehicles. It has become desirable toextend mobile telephone service to other public transportation servicessuch as taxicabs, bus, railroad, and rent-a-car services. Additionally,temporary fixed installation of radiotelephone service such as at tradeshows or fairgrounds has become desirable. In so extending the service,those entities providing the service must address the problem ofcollecting payment for the telephone service provided Collection of coinand currency in pay phones placed on inter-urban trains has been knownfor a long time but adequate compensation for a long distance call or acall of long duration is often times difficult to collect in such a payphone. The advent of credit cards with magnetic or other means of datastorage has enabled the credit caller the opportunity to charge hiscalls to his credit card thereby assuring the telephone service providerpayment for toll or metered telephone calls.

Generally, the procedure for enabling the credit card telephone is tohave the potential user run his credit card through a magnetic stripereader. This first step reads at least one "track" of the magneticstripe (usually "track two") which includes, inter alia, identificationof the card and expiration date. Further definition of magnetic stripeencoding may be found in ANSI X4.16-1983 "American National Standard forFinancial Services - Financial Transaction Cards - Magnetic StripeEncoding". A telephone call is then placed to the credit call providerand the track two information is read to the computer of the credit callprovider. A check is then made of the card validity and expiration dateand if no reason exists for denying service, a single telephone call isallowed. In this form, the operation is similar to that of an automaticteller machine (ATM). The single telephone call is dialled by the credituser to the computer (or telephone switch) of the credit call providerwhich subsequently redials the call to the public switched telephonenetwork (PSTN). When the user terminates his call, the credit callprovider senses the end of the call. The credit call provider can thencalculate directly the duration of the call, any toll or meteredcharges, and any air time charges accumulated through the use ofradiotelephone circuits. The disadvantage of this operation is that thecredit call provider must maintain telephone switching equipment whichmust redial the user's call and must procure adequate input and outputtelephone trunks to carry the expected amount of telephone traffic.

Others have suggested that the credit call provider only needs tomonitor the start and completion times of the user correlated to theparticular mobile unit used in making the credit card call. In fact, aproperly synchronized credit card mobile telephone system would needonly the starting time (or the completion time) of each credit card useand the mobile telephone unit identification. Any calls made between thestarting time of a first credit card authorization and the starting timeof a second credit card authorization would be billed to the firstcredit card. Thus, the credit call provider would not have to maintain atelephone switch or lease a large number of input and output telephonetrunks. It is not clear, however, that the equipment which interfaceswith the credit card user can provide a telephone service which appearsto the user to operate in a "normal" telephone mode, with each telephonecall being made in a consistent and familiar manner.

In other credit call schemes, modifications have been suggested to thestandard signalling protocol of the radiotelephone system which create anon-standard system. Further, if a standard system of signalling ismaintained, it is desirable that a credit card data transmissiontechnique be employed which correctly transmits the credit cardinformation error free.

SUMMARY OF THE INVENTION

Therefore, one object of the present invention is to read andcommunicate credit card information from a mobile radiotelephone unit toa registration computer.

Another object of the present invention is to transmit the credit cardinformation with a minimum of errors.

A further object of the present invention is to reduce the messagelength of the data transmission.

Accordingly, these and other objects are achieved in the presentinvention which encompasses the method and apparatus for reading acredit card identification number at a mobile radiotelephone unit andcreating a data field from the read identification number. A message issubsequently generated for radio transmission from the mobile unit andutilizes a format which comprises an opening flag of at least one SOHcharacter, a data length character, a message type character, theidentification number data field, at least one cyclic redundancy codecharacter, and at least one longitudinal redundancy check character.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a system which may employ the presentinvention.

FIG. 2 is a block diagram of a mobile unit for use in the system of FIG.1 and which may employ the present invention.

FIG. 3 is a block diagram of a logic unit which may be utilized in themobile unit of FIG. 2 and which may employ the present invention.

FIG. 4 is a block diagram of a control unit for the mobile unit of FIG.2 and which may employ the present invention.

FIG. 5 is a physical design of the control unit of FIG. 4.

FIG. 6 is a state transition diagram which illustrates the states andstate changes which form part of the present invention.

FIG. 7 is a state transition diagram which illustrates the states andstate changes which may occur when a credit card is slid through a cardreader in accordance with the present invention.

FIGS. 8A, 8B, and 8C are a state transition diagram which illustrate the"Pls Wait" state of FIG. 6.

FIG. 9 is a diagram showing the composition of a data message employedin the present invention.

FIG. 10 is a flowchart showing the process employed in the presentinvention in recovering the data message in both the mobile unit and theregistration computer.

FIG. 11 is a flowchart of the Getchar subroutine utilized by the processof FIG. 10.

FIGS. 12A and 12B are flowcharts of the message transmission processemployed in the present invention.

FIG. 13 is a flowchart of the remote programming of telephone numbersemployed in the present invention.

FIG. 14 is a flowchart of the repertory telephone number file recallprocess employed in the present invention.

FIGS. 15A and 15B are flowcharts of the remote programming ofregistration telephone numbers employed in the present invention.

FIG. 16 is a flowchart of the process employed by the present inventionto remotely retrieve the contents of a selected mobile unit memorylocation and transmit the contents to the registration computer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A greatly simplified illustration of a radiotelephone system which mightemploy the present invention is shown in FIG. 1. A mobile unit 101within radio transmission and reception range of a fixed site 103 whichtypically includes one or more radio transmitters, one or more radioreceivers, antennas and transmission facilities, site computer controlequipment, and interconnection to a mobile telephone exchange 105. Suchfixed site equipment may be of the type described in "Dyna T*A*C LDSeries Cellular Mobile Telephone Integrated Base Station", InstructionManual No. 68P81060E30-C, 1986, Motorola Technical Writing Services,1301 E. Algonquin Road, Schaumburg Ill. 60196. A mobile telephoneexchange may be of the EMX type described in Instruction Manual No.68P81052E05-A, 1985, Motorola Technical Writing Services, 1301 E.Algonquin Road, Schaumburg Illinois 60196.

The mobile exchange 105 switches calls between mobile telephone unitsand between the land line public switched telephone network (PSTN) andmobile units such that the operation is virtually indistinguishable fromstandard telephone operation. In a cellular mobile telephone system, aplurality of fixed sites may be connected to one or more mobileexchanges which further serve to mediate handoff of a radiotelephonecall as the mobile unit travels from one radio coverage area to another.

In a radiotelephone system which provides pay telephone service by usingconventional credit cards as the means for extending credit to theradiotelephone user, it is necessary to check the validity of the creditcard (the paying history, maximum credit to be extended, expirationdate, etc.) before authorizing the credit extension. Further, sometechnique of monitoring the call duration and other charges which areaccumulated against the telephone call and applying the charges(correctly) against the right credit card must be employed. Such tasksare assigned, in the present invention, to a registration computer 107which may be a part of a separate billing exchange 109, part of themobile exchange 105, or a stand-alone computer accessed by predeterminedtelephone trunks assigned certain telephone numbers. The presentinvention addresses the third alternative in the discussion of thepreferred embodiment although the invention may be employed in the firstand second alternatives as well.

The mobile unit typically would include a mobile transceiver and acontrol unit having special adaptation for using credit card readingdevices. A cellular mobile transceiver suited for use with the presentinvention is described in "Dyna T*A*C Cellular Mobile Telephone",Instruction Manual No. 68P81066E40-C, 1985, Motorola Technical WritingServices, 1301 E. Algonquin Road, Schaumburg Ill. 60196. A generalizedblock diagram of a mobile unit is shown in FIG. 2.

In FIG. 2, a mobile transceiver 201 is coupled to a control unit 203 toprovide the essential functioning elements of the mobile unit 101. Theprimary user interface will be with the control unit 203 as he provideshis credit card for identification, dials telephone numbers, listens,and speaks. The control unit 203 will be described in more detail below.The mobile transceiver 201 consists of the basic blocks of a radioreceiver 205, a radio transmitter 207, a logic unit 209 (whichcoordinates the activities of the receiver 205, transmitter 207, andcontrol unit 203 and which utilizes a microcomputer to process andmaintain radiotelephone calls), a frequency synthesizer 211 (which,under the direction of the logic unit 209, selects the proper operatingfrequency of the receiver 205 and the transmitter 207), and a duplexer213 (which couples the receiver 205 and the transmitter 207 to anantenna 215).

The logic unit 209 of the mobile transceiver 201 is further described inthe block diagram of FIG. 3. A microprocessor 301 (which may be a type68HC11 or similar device) utilizes ROM 303, RAM 305, and EEPROM 307memory to process and store the necessary program steps and input andoutput data for control of the remote unit in the cellular system.Interface to the radio frequency components (receiver 205, transmitter207, and synthesizer 211) is realized through a control circuit 309which further has the capability of providing received data and receivedsupervisory audio tones (SAT) to a signal interface circuit 311. Thesignal interface 311, under control of microprocessor 301, providesdata, SAT, and dialing tone (DTMF) direction to control circuit 309 forsubsequent transmission by transmitter 207. Data and control interfaceis realized from microprocessor 301 to the control unit 203 via buslines TRU, CMP, and RTN in a manner more fully described in U.S. Pat.No. 4,369,516. Similar interface between a transceiver logic unit andassociated control unit are described in U.S. Pat. Nos. 4,398,265 and4,486,624.

The control unit 203 is shown in block diagram form in FIG. 4. A cradlemicroprocessor 401 (which may be a 68HC11 or equivalent type havinginternal EEPROM) is coupled to the three wire bus lines TRU, CMP, andRTN from the logic unit 209 microprocessor 301 and executes the programsteps stored in EPROM memory 403. A second microprocessor 405 is locatedin a handset portion 407 of the control unit and communicates with thecradle microprocessor 401 via another three wire bus. The handsetmicroprocessor 405 strobes the pushbutton keys of a telephone dialingkeypad 409 for any dialing activity by the user and provides outputinformation to handset indicators 411 and a multidigit display 413through display drivers 415.

Audio is routed from the radio receiver 205 to the transducer 417 in thehandset via the receiver mute switch 419 and multiplexer 425 in thecradle (which is controlled by the cradle microprocessor 401). Thereceived audio is also routed to the cradle speaker 421 via audioamplifier 423 and multiplexer 425 for inclusion of user feedbackgenerated by tone generator 427.

Audio is routed from the handset microphone 429 through cradlemicroprocessor 401 controlled muting switch 431 to the radio transmitter207 for transmission. Data for registration and control generated bymicroprocessor 401 for transmission is converted to a radio-compatibleformat by modem 433. Data received by the radio receiver 205 during theregistration sequence and other credit card control processes isconverted by modem 433 and presented to cradle microprocessor 401 forfurther processing.

Information is read from the appropriate track of a magnetically encodedcredit card stripe by a conventional card reading mechanism 435. Thisinformation is presented to the cradle microprocessor 401 for use whichwill be described later. Additional inputs are received from the handseton-hook/off-hook hookswitch (HKS), vehicle door switch, and telephonelock switch. Indicators on the cradle are driven by cradlemicroprocessor 401 via latch circuit 437.

One physical implementation of a control unit 203 is showndiagramatically in FIG. 5. This unit is similar to that shown in U.S.patent application No. 042,787 filed on Apr. 27, 1987 in behalf ofPulio, et al. The control unit may consist of a cradle 501, a handset407, and a magnetic stripe card reader 435. Of particular interest tothe user are the keypad 409 (which utilizes, in the preferredembodiment, 12 keys corresponding to the numbers 0 through 9 and the "*"and "#" keys arranged in standard telephone orientation the vacuumfluorescent display 413 (which in the preferred embodiment has thecapability of displaying 14 characters of 7 segments each, althoughother types of displays with other combinations of characters andsegments may be employed), and operational function lights "In Use" 511,"No Svc" 513, and "Roam" 515. Additional indicators are located on thecradle 501: a "Slide Card" light 517, a "Pls Wait" light 519, a "LiftRcvr" light 521, and a "Sorry" light 523. The telephone lock switch 525is also located on the cradle 501.

Referring now to a preferred embodiment shown in FIG. 6, which is astate transition diagram commonly used in complex system process flow(see "Introduction to Switching Theory and Logical Design", Fredrick J.Hill and Gerald R. Peterson, John Wiley & Sons, 2nd Edition, 1974-pages241-306), when the control unit is turned on, a flashing "hello busy" asshown in state 601 is placed in the display 413. After approximately twoseconds of information exchange with the mobile telephone transceiver201, the control unit microprocessor 401 electronically locks thetransceiver 201 via the logic unit 209 (as shown in state 603) and theprocess goes on to state 605. In this state the slide card light 517 iscaused to flash and a steady "hello" is placed in the display 413.Twenty-five seconds later, the process goes to state 607. In this statethe slide card light 517 is steadily illuminated as is the "hello" indisplay 413. If a card is slid through the card reader 435 by the userduring this state, the "pls wait" flashing state 609 is entered. State609 is further described in conjunction with FIG. 7.

In FIG. 7 the card is checked (701) against two locations in memoryEEPROM internal to microprocessor 401. The first location is designated"last valid card" which is the last card to have been registered fromthis unit. If the contents of the "last valid card" match theidentification of that card, the transceiver 201 is unlocked at 703 andthe lift handset state 705 is entered. The second location against whichthe card is checked is designated the "last invalid card". The lastinvalid card is the last card to have attempted a registration via thismobile unit and for which the registration computer 107 at the billingexchange 109 denied telephone service access. Such a service denialwould occur if, for example, a stolen card is slid through the cardreader 435 and the identification matches the "stolen card" records atthe registration computer 107. At this point the process proceeds to the"access denied" state 707. This "access denied" state prevents aregistration call and access to the billing exchange is thereby denied.Such a feature reduces radio air time usage by eliminating needlesschecking by the registration computer 107 of cards already shown to beinvalid.

If the card identification is in neither mobile unit memory location,the expiration date of the card is checked as part of the check cardstate 701. If the card has not yet expired, the process proceeds tounlock (at 709) the transceiver logic unit 209 and place a call to theregistration computer 107. This leads to state 711, where the "Pls Wait"light 519 is flashed on the control unit 203.

The registration process is controlled by the cradle microprocessor 401and its associated memory 403. In a preferred embodiment, threetelephone numbers are stored for use in calling the registrationcomputer 107 as part of the registration process. A first step in theprocess (at 713) is the dialing of registration number one. This isaccomplished by causing the transceiver logic unit 209 to retrieve thetelephone number from microprocessor 401 memory EEPROM. The transceiver201 is then caused to transmit and receive in conventional fashion.Also, as part of step 713, the unit recalls the call timer "odometer"(which is the cumulative number of minutes of air time used by thistransceiver since the transceiver was manufactured). This "odometer"information can be used by the registration computer to determine howmany minutes of user-placed telephone calls have occurred since the lastregistration. When carrier is received back from the registrationcomputer 107 the "card information" message is sent (at 715) to theregistration computer 107. The "card information" message essentially istrack two of the credit card magnetic stripe; addition description ofthe "card information" message is given below. When an acknowledgemessage is received from the registration computer 107, another message,which is referred to as the "mobile information" message, is transmittedby the mobile unit at 717 to the registration computer 107. The "mobileInformation" message includes such data as the mobile telephone number,the unit ID, the revision ID, the call timer "odometer" and othersimilar information. In the preferred embodiment both the "cardinformation" and the mobile information message may be repeated up to 5times if the previous transmission is not acknowledged.

In response to the mobile information message the registration computer107 would transmit an access message which would be received by themobile transceiver at 719. The access message includes with it a"calendar" which is a numerical representation of month and year. In thepreferred embodiment, March, 1987 would be sent as 8703. This calendaris used to update (at 721) the calendar in the transceiver control unit203. The calendar in the control unit 203 is used to check the creditcard expiration date for assurance that the card validity has notexpired.

At the conclusion of the access message, the registraitin computer hangsup and the entire mobile unit registration telephone call is terminated.A unique feature of the present invention is that which allows the userof the credit card mobile telephone to use the telephone to make callsin a manner which is identical from one call to the next. Accordingly,the process of credit card registration and validation is separate fromthe process of placing a telephone call. The mobile transceiver 201, inresponse to the access message, clears two memory locations at 723.Resident in the first memory location is the last phone number dialed bya user and resident in the second memory location is the number of callsplaced by the last user. In addition an answer call flag and a roamingcall flag are cleared.

Following the "access accepted" path, the process places the credit cardidentification in the last valid card memory location. This allows theunit to validate this last used card when the user slides this cardthrough card reader 435 without making a registration call to theregistration computer 107 even though the transceiver logic unit 209were returned to the locked state. After the last valid card memorylocation is set at 725, the "lift handset" state 727 is entered. Theuser can place a phone call at this point.

Returning to the unlock block 709, if the mobile transceiver 201 isroaming but is not permitted to make registration calls while it isroaming, the process proceeds to the "sorry no access" state 729 and itwould light the roam light 515. (Roaming is the operation of a mobileradiotelephone in a radio service coverage area different from that inwhich the radiotelephone is originally registered. For example,operation in another city served by a different radiotelephone service).Similarly, if service is not available at all, the system would end upin state 729. In effect state 729 tells the user to try again later.

The next possible variation, proceeds through the "pls wait" state 711and into the "dial registration number one" activity 731. If 25 secondspass and the registration computer 107 data carrier has not beendetected, the call is terminated and the "dial registration number two"activity 731 is entered. If data carrier is detected, the processcontinues to "send card information" (at 715). However, if data carrieris not detected, after another 25 seconds, the call is terminated and"dial registration number 1" is dialed at 733. Similarly, if datacarrier is found at this point, the process returns to "send cardinformation" at 715. If data carrier is not detected after 25 seconds,the transceiver logic unit 209 is relocked at 735 and the "sorry, noaccess" state 737 is entered. (The dialing sequence just described is astandard registration call dialing sequence. Other sequences may beemployed for different circumstances. For example, if the unit isroaming and roam dialing sequence is enabled, then the registration calldialing sequence could be another sequence of telephone numbers).

Returning to the "send card information" activity at 715, if after 5times, the message cannot be sent or if data carrier is lost while theinformation is being sent, the call is terminated and the sameregistration is redialed (at 739). If data carrier is detected, the"send card information" block 715 is entered again. If data carrier isnot detected after 25 seconds, the transceiver logic unit 209 is locked(at 735) and the process goes to the "no access" state 737. A similarprocess is employed to transmit the "mobile information" message (at717). The process tries 5 times; if data carrier is lost and aregistration number has been dialed more than twice with loss of datacarrier, the process will end in the "no access" state 741.

After sending the "mobile information" message (at 717), the processexpects one of three possible responses from the registration computer107: an "access accept" message, a "deny access" message, or an"acknowledge" message. If the acknowledge message is received, the unitwill wait as long as data carrier is detected for a subsequent accept ordeny message. The acknowledge message (ACK) would be experienced if theregistration computer 107 recognizes that it will take longer than 3seconds to look up information in, for example, the stolen card files.In essence, more than two registrations calls results in a locking ofthe mobile transceiver (at 743) and an entry into the "no access" stateat 745.

Upon transmitting an "access accept" message or a "deny access" messagethe registration computer 107 can send other messages which, in thepreferred embodiment, might include messages such as a request formobile radiotelephone status information, a reprogramming of mobileradiotelephone status, or a change in the contents of a repertorytelephone number location. Message block 747 provides the opportunity todo so. If a "deny access" message is received, the card number ID thatwas read from the card is stored (at 749) in the "last invalid card"memory. The mobile unit is subsequently locked (at 751) and the "accessdenied" state 753 is entered. If the same card is wiped again, theprocess immediately goes to the "access denied" state 707 withoutplacing another registration phone call.

Referring back to FIG. 6, after the mobile unit power is turned on, theprocess enters and leaves the "hello-busy" state 601, locks at 603, andstops in the slide card flashing "hello" state 605. If the credit cardis wiped in state 605, the process will go directly to the "pls wait"flashing state 609 as described in FIG. 7. Other possibilities of actioninclude the pressing of a key on dialing pad 409 which results in aflashing slide card light 517. This indication is basically to instructthe user to slide a credit card at this time.

If the unit is in state 607 and a detection of the vehicle door beingopened and closed occurs, the process goes to state 605 and the "slidecard" light 517 is flashed for 25 seconds. This is a welcome message toa new user of the system. From state 607, if the handset 407 is takenoff hook, the process goes to state 610 which has a flashing "slidecard" light 517 and a "hello" in the display 413. Pressing any key onkeypad 409 will hold the process in this state. If the handset 407 isplaced on hook, the process will return to state 607.

Another exit from state 610 (where the handset is off hook) may be thedialing of 911. If 911 dialing is enabled and 911 is entered on thekeypad 409, the mobile unit will unlock (at 613), when the "no svc"light 513 is extinguished. A call is placed to the 911 emergency number(at 615). When the emergency call is ended, the unit will lock (at 617)and return to state 607. Similarly, if 611 dialing is enabled and 611 isentered on the keypad 409, the unit will unlock (at 619) a call isplaced to the number which is stored in microprocessor 401 internalmemory EEPROM referred to as the 611 number (at 621). At the conclusionof this call, the unit is locked (at 623) and the process returns tostate 607.

If keypad keys are pressed while the process is in state 607, theprocess goes to state 625 where the "slide card" light 517 is flashedand "hello" is placed in the display 413. After the user stops pressingkeys and 5 seconds transpires, the process returns to state 607. Also,the handset 407 is taken off hook while the process is in state 607, theprocess proceeds to state 610. If a credit card is subsequently slid,the process goes to the "pls wait" light 519 flashing state 609.

Turning now to FIG. 8A and starting at state 711 where the "pls wait"light 519 is flashing, several paths exit the state. The first path isfollowed if the card track two was not read properly; the system returnsto state 607. The second path is followed if the card data matches thelast invalid card. The process goes to the "sorry access denied" state801 for 5 seconds and then returns to state 607. Similar steps arefollowed if the card validity date has passed. If the registrationcomputer 107 tells the system that access is denied on the card, themobile logic unit 209 is locked (at 803), the "access denied" state 801is entered for 5 seconds, and the process returns to state 607 after the5 seconds. If sufficient data errors are experienced with the connectionto the registration computer 107 and the call is never successfullycompleted, the mobile logic unit 209 is locked (at 805), "no access" isentered in the display 413 and the "sorry" light 523 is illuminated(state 806) for 5 seconds before returning to state 607. If the unit isroaming and roam is not permitted or if there is no service available,the control unit 203 would be placed in state 807 ("no access" indisplay 413, illuminated "sorry" light 523 and an illumination of eitherthe "no svc" light 513 or the "roam" light 515) to indicate the reasonof failure to the user. Five seconds later the process locks the logicunit 209 (at 809) and returns to state 607.

Assuming the card is passed by the registration computer 107 and theprocess progresses from the "pls wait" state 711, the access acceptedpath leads to state 811, the "lift hset" state shown in FIG. 8B. In thisstate, the "lift rcvr" light 521 flashes and a time-out timer circuit inthe control unit 203 is reset. If no service exists in the geographicarea where the mobile transceiver is located or if the mobiletransceiver is roaming, the appropriate light is lit on the handset 407.

Normally, service is available and the transceiver is not roaming. Ifthe user takes the handset 407 off hook, the process goes to state 813where "dial" would be placed in the display 413, dial tone will begenerated by the control unit 203, and the process waits for the user todial digits on the keypad 409. At this point, if the user dials atelephone number, the digits will be echoed to the display 413, (at 815)and the dial tone is turned off with the first depressed key. Uponcompletion of dialing and termination of a 5 second waiting period, thecall is placed to the dialed umber (at 817). The control unit 209 lastnumber dialed (part of microprocessor 401 EEPROM) is updated to thisphone number. When the user ends this call, the process either returnsto the "dial" state 813 if the handset 407 is off hook or returns to the"lift hset" state 811 if the handset 407 is on hook. If the call isterminated by placing the handset 407 on hook, the mobile transceiverlogic unit 209 is placed in a locked state at 818 and the system goes tostate 607. In the preferred embodiment there are four programmable locktriggers and one non-programmable lock trigger in which the mobiletransceiver logic unit 209 is placed in an electronically lockedcondition which can be unlocked by an access command from theregistration computer. The four triggers are: (1) a time out locktrigger with a preprogrammed time out period, programmed in minutes from1 through 255; (2) a lock trigger which activates each time the handset407 is placed on hook; (3) a vehicle door open detector which triggersthe lock any time the door is opened; and (4) a power-up lock whichcauses the mobile transceiver to be in the lock state when power isapplied to the transceiver. The non-programmable lock trigger isactivated from the "lock" switch 525 on the control unit cradle.

Returning to the "lift hset" state 811, if there is no service or if themobile transceiver is roaming when roam is not permitted, state 819places "no access" in the display 413 accompanied by illumination ofeither the "no svc" light 513 or "roam" light 515. Dial tone, however,is not activated in state 819 as an indication that calls cannot beplaced. If the handset 407 is placed back on hook, the process willreturn to state 811, "lift hset". If the service becomes available or ifroaming is permitted, the process will immediately go to the "dial"state 813 while the handset 407 is still off hook. The user can thenplace a call. If from either the "dial" state 813 or the "no access"state 819 no further actions are taken by the user for 25 seconds, theoff hook siren is activated (at 821) as an indication that the unit isnot correctly on hook. Pressing a key at this state returns the processto state 813 where digits are echoed to the display 413. From this"dial" state 813, if the user presses * button, the "dial" in thedisplay 413 would momentarily blank and the dial tone would momentarilyvanish, to give an indication to the user that he has just cleared thecontrol unit states. If he had dialed some digits prior to pressing thebutton, the digits will be erased and dial tone would return. Pressing aredial key will cause the control unit 203 to redial the number storedin repertory memory location 00 of the mobile telephone, the lasttelephone number to be dialed. The call will be placed immediatelyrather than waiting for 5 seconds. Another exit from state 813 is thatof dialing 611 (to obtain repair and information intercept operator).Upon detecting 611 (at 823), a call will be placed to the telephonenumber which is stored in the microprocessor 401 memory EEPROM locationcorresponding to the 611 dialed number. At the conclusion of the 611call, the process goes back to the "lift handset" state 811 if thehandset 407 is on hook.

Incoming calls are handled in several ways. If the process is at the"lift hset" state 811, and a call is received, the process goes to state825 "lift hset" as shown in FIG. 8C. The word "call" is placed into thedisplay 413, the "lift rcvr" light 521 will remain flashing, and anaudible ring will be generated. If the user goes off hook, the processmoves to the "call" state 827, where it remains for the duration of thetelephone call. When the user goes back on hook after 15 seconds, theprocess returns to the "lift hset" state 811 by passing through the"dial" state 813. If the user hangs up in less than 15 seconds, thecontrol unit 203 will test for received data carrier at 829. If suchcarrier is not detected within 5 seconds, the process returns to the"lift hset" state 811. However, if data carrier is detected, the handsetaudio will be muted at 831 and the process proceeds to state 833. Instate 833, "busy" is placed in the display 413 and any messages comingfrom the registration computer 107 will be received by the cradlemicroprocessor 401 via modem 433. Any appropriate return messages willbe sent back to the registration computer 107 at this time. At theconclusion of this type of call, the process returns to state 607 withthe phone "locked".

Returning to state 825 in FIG. 8C, if the user does not answer thecalled phone within 15 seconds, the process goes to state 835. Thecradle microprocessor 401 will answer the call, mute the handset at 831,and go to the "busy" state 833. Again, at the conclusion of this call,the process returns to state 607 with the phone locked. It is assumed atthis point communications will take place between the cradlemicroprocessor 407 and the registration computer.

The process may await an incoming call in any of the slide card statesof FIG. 6 in the "any slide state" block 837 of FIG. 8C. If a call comesin, a 15 second timer will be reset at 839 and state 841 is entered. Inthis state, the "slide card" light 517 will continue to flash and "call"will be placed in the display 413. If the call ends before anything elsetakes place, the process returns to state 607. However, if the 15 secondtimer times out, the mobile transceiver logic unit 209 will be unlockedand state 835 enables the cradle microprocessor 401 to answer the call.Alternatively, the user can slide a credit card through the card reader435 and the card is checked at 845. If the card ID matches the lastvalid card, the process unlocks the mobile transceiver logic unit 209(at 847) and goes to state 825, if the handset 407 is on hook. If thehandset 407 is off hook, the process enters state 827, the call state.

Referring now to FIG. 9, a message format employed in the preferredembodiment is illustrated in block form. It is important that theinformation encoded on the credit card be correctly transferred to theregistration computer 107 for validation and billing. If the credit cardinformation is received incorrectly, either the wrong person or no oneis billed for the subsequent phone calls.

A variable length message format and signalling scheme transmitted inasynchronous format using one or more bytes having a start bit, eightdata bits, and one stop bit is employed in the preferred embodiment. Thevariable length message format improves the probability of successfullyreceiving messages in a fading environment because the message is onlyas long as it needs to be rather than an arbitrarily selected fixedlength. The message includes two forms of error checking - a cyclicredundancy check (CRC) and a longitudinal redundancy check (LRC). Thecombination of the CRC and the LRC should yield a delivered bit errorrate (BER) better than 10⁻⁷.

As shown in FIG. 9, the opening flag consists of two start-of-header SOHcharacters (ASCII $01 in the preferred embodiment). The length of thedata field is identified by "data length" consisting of a one bytecharacter. The message type, which is identified by a unique number from0 to 255, is identified by the next character byte in the format. Thevariable length data field follows and consists of from 0 to 255 bytesof information. The CRC is calculated over the "data length", "messagetype", and "data field" bits using a CRC-16 polynomial. In this format,a sixteen bit value is transmitted in two characters (CRChi/CRClo)withthe most significant byte transmitted first. The CRC is conventionallycalculated by dividing the data message bit pattern by the CRC-16polynomial and saving the remainder as a sixteen bit value CRC. The LRCis an odd parity check calculated on columns over the "data length","message type", "data field", and "CRC" fields. The LRC is generated byexclusive OR-ing each byte of the message with the last value of the LRCand the result is stored as the current value of LRC.

There are three basic message categories employed in the preferredembodiment: (1) typical mobile-to-base; (2) typical base-to-mobile; and(3) setup. All of the parameters required by the mobile unit foroperation can be programmed by the registration computer 107 using setupmessages. The messages employed in the preferred embodiment aresummarized as follows:

    ______________________________________                                        Message  Data                                                                 #        Length      Message Contents                                         ______________________________________                                        MOBILE-TO-BASE                                                                1        20          credit card track 2                                      BASE-TO-MOBILE                                                                2        2           access accepted, calendar                                3        2           access denied, calendar                                  4        0           terminate                                                5        1           return 1 specified message                               SETUP                                                                         6        5           registration phone #1                                    7        5           registration phone #2                                    8        5           registration phone #3                                    9        13          credit card table                                        10       10          last invalid card used                                   11       6           repertory location, phone #                              12       l           acknowledge message type                                 13       0           negative knowledge                                       14       2           lock options, time out time                              15       1           roam options                                             16       5           611 phone number                                         ______________________________________                                    

The message number may be arbitrarily selected by the designer of themessage communication system. Likewise the number of messages may bemore or less depending upon the needs of the system.

Referring now to FIG. 10, the message protocol employed in the presentinvention is diagrammed in flowchart form. Generally, the messageprotocol calls for a retransmission of a message if it is notacknowledged within, for example, three seconds or if a negativeacknowledge (NAK) is received. If the CRC or LRC check characterscalculated by the process do not match that sent by the transmitter, themessage will be NAK'ed. Five transmissions are attempted for eachmessage. A properly received message may be acknowledged by anacknowledge message (ACK) or by other specific messages.

The mobile transceiver transmits the credit card information read from auser's credit card magnetic track, information identifying the mobileunit, and other miscellaneous information to the registration computer107 as described above. The registration computer 107 updates themicroprocessor clock in the control unit and, inter alia, allows ordisallows the user to place calls. The registration computer 107 mayalso program the features of the control unit microprocessor system toprovide remotely controlled features of the credit card system andprogram the repertory phone number list of the mobile transceiver logicunit 209. The control unit 203 needs to know such information as thetelephone numbers of the registration computer, the prefixes of thecredit card identification which should be accepted by the unit, andwhich lockout triggers should be enabled.

The flowchart of FIG. 10 starts at the "Receive" process subroutine incradle microprocessor 401 in which the reception timer is reset at 1001.The "Receive" process is utilized at both the mobile unit 101 and theregistration computer 107 to recover the data message with a minimumnumber of errors. A test is made at 1003 to determine if the timer hastimed out (exceeded 5 seconds in the preferred embodiment) and if it hastimed-out, an error is flagged at 1005. If the timer has not timed-out,the "Getchar" subroutine is entered at 1007. Upon return from the"Getchar" subroutine, a test is made at 1009 of the received characterto determine if the character is the SOH ($01) character expected at thebeginning of the message. An improper character returns the process tothe timer test of 1003. A proper character leads to a second calling ofsubroutine "Getchar" at 1011 and a second test for the SOH character at1013. A second correct character at the beginning of the message causesthe process to clear the CRC memory and a preloading of $FF in the LRCmemory (at 1015); an improper character returns the process to the timertest of 1003. The "Getchar" subroutine is again called and the length ofthe data field is established by the third byte of the message. The datalength is set by the character returned by the "Getchar" subroutine (at1017). The CRC and LRC memories are updated at 1019 before the processmoves to the message bytes acquisition shown in FIG. 11.

The "Getchar" subroutine is also shown in FIG. 10. A test of receivedcarrier is first made at decision block 1023. Lack of data carrierreturns the process to the timer test block 1003; carrier detectionresults in a test of whether a character is received within 500milliseconds (at 1025 and 1027). The received character is returned tothe calling subroutine. The timer is reset at 1029 before a test for aframing error is made at 1031. A framing error consists of a missed stopbit where such a miss causes the process to return to the timer test ofblock 1003 and no framing error causes the process to return to the"Getchar" subroutine calling point in the process.

The message type character is obtained by calling the "Getchar"subroutine from block 1101 of FIG. 11. Other initializations of thepremessage state are made in block 1101. So long as the message counteris less than the established data length, the message counter test ofdecision block 1103 allows the message storage location to fill with themessage character by character with repeated calls of the "Getchar"subroutine and the calculation of CRC and LRC to proceed with eachmessage character (at 1105). When the message count and the data lengthare equal, the two CRC characters are obtained from successive calls ofthe "Getchar" subroutine and the LRC character is obtained from a thirdcall of the "Getchar" subroutine (at 1107). The CRC characters are thenchecked for correlation to the CRC calculated during reception of thedata length, data type, and data message bytes at decision block 1109. Apositive result causes the process to test the LRC character against thecalculated value at 1111. A positive result causes an ACK to betransmitted (at 1113) before the process returns to other tasks. Ifeither the CRC check or the LRC check are not positive, a test is madeat 1115 for an idle condition: no received characters during the idleperiod. Thus, if no characters are received for 500 milliseconds, a NAKis transmitted at 1117 and the process returns to other tasks.

The process of message transmission is shown in the flowchart of FIG.12. The process shown may be employed by both the mobile unit 101 andthe combination of fixed site equipment 103 and registration computer107. The mobile unit 101 typically generates credit card track messageswhile the registration computer typically generates control messages (asdescribed previously). Thus, the data for the mobile unit 102 messageare input from the reading of track two of the credit card when the userwipes the card through the card reader 435 of the control unit 203.Likewise, the data for the base message is input from the internalfunctions of the registration computer 107.

The data transmission process, "Transmit" commences with the storage oftwo concatenated start-of-header (SOH) characters ($01) in the messagebuffer of the process (at 1201). The CRC and LRC storage locations areinitialized at 1203. In order to generate the "Data length" fieldcharacter, the message characters are counted and the data lengthcharacter is created (at 1205). The cyclic redundancy code (CRC)character storage and the longitudinal redundancy check (LRC) characterstorage is updated with the data length character and the data lengthcharacter is shifted into the message buffer (at 1207). The message typefield character is created (at 1209). The CRC and LRC character storageis updated and the message type character is shifted into the messagebuffer (at 1211).

The data message itself is shifted into the message buffer one characterat a time, thereby enabling the updating of the CRC and LRC characterson each message character. This message shifting is shown in the loop of1213, 1215, and 1217. When the message length counter (MSGCOUNT) equalsthe data length character (DATALENGTH) the loop is exited (at 1213) andthe CRC and LRC characters are shifted into the message buffer followingthe update of the LRC character from the CRC characters (at 1219). Thecontents of the message buffer are then transmitted by the radiotransmitter (at 1221) and the 3 second timer is reset at 1223.

The "Transmit" subroutine then looks for an message transmitted backfrom the mobile transceiver at decision block 1225 while waiting for the3-second timer to time out at 1227. If the message contains an ACK (oris itself an acknowledgment), as determined at decision block 1229, theprocess returns to other tasks. If an ACK is not received in a messagefrom the mobile or if the timer times out without receiving a messagefrom the mobile transceiver within three seconds, a test of the numberof retransmissions is made at block 1231. If the number of retries isless than five, the "Transmit" subroutine is called again, at 1233. Ifthree retries have been attempted without acknowledgment, an error isflagged and the process returns to other tasks. The process may thenhang up and try again.

The system of the present invention has the unique capability ofaccepting telephone numbers and other programming information at themobile unit for storage in the logic unit microprocessor 301 and thecradle microprocessor 401 when transmitted from the base. Further, theprogrammed information may be recalled from the mobile unit memory andrepeated to the base. An example of this remote programming of telephonenumbers is shown in FIG. 13. The process is initiated at theregistration computer 107 where the mobile unit is called (over one ofthe telephone trunks linking the registration computer 107 to theradiotelephone system) and data carrier is generated, at 1301. Once thetelephone connection is complete and the mobile unit is rung (at 1303)and answers (at 1305), the cradle microprocessor 401 detects the datacarrier and generates data carrier (at 1307) via modem 433. This mobileunit generated data carrier is transmitted via the mobile telephone callto the registration computer where it is detected (at 1309). In theexample of FIG. 13, the registration computer 107 generates a datamessage #11 (as defined previously). Message #11 includes the digits ofa telephone number to be stored in the memory of the mobile unit and thelocation number at which the telephone number is to be stored (at 1311).The message of block 1311 is transmitted to the mobile unit where themessage is received (at 1313), the telephone number is stored in thedesignated memory location (at 1315), and the message is acknowledged(at 1317) in a manner described previously. The acknowledgment isreceived at the registration computer (at 1319) and the registrationcomputer 107 sends (at 1321) a termination message, (#4) to the mobileunit. Upon receipt of the termination message, the mobile unit hangs up(at 1323). The registration computer hangs up (at 1325) after thetransmission of message #4. If an acknowledgment of message reception isnot received (at block 1319) by the registration computer 107 in apredetermined amount of time selected by the system operator, theprocess of sending message #11 is repeated.

The registration computer 107 may request the contents of a selectedtelephone number memory location to be read with the use of message #5.This process is shown in FIG. 14. The mobile unit is called (at 1401) bythe registration computer, rings (at 1403), answers (at 1405), detectsdata carrier and generates data carrier (at 1407), and transmits thedata carrier to the registration computer. The registration computer 107detects carrier from the mobile unit(at 1409) and progresses to sendingthe message #5 including the data message at 11,20 (at 1411), whichcauses he repertory memory location 20 to be read upon receipt of themessage by the mobile unit (at 1413). The mobile unit then responds witha transmission of message #11 including the digits of the telephonenumber stored at repertory location 20 (at 1415). The registrationcomputer receives the message (at 1417), transmits a termination message#4 (at 1419), and hangs up the call (at 1421). The mobile unit receivesthe termination message and hangs up (at 1423).

The registration computer 107 may also load other parameters into thememory of the mobile unit such as shown in the example of FIG. 15. Theregistration computer places a call to the mobile unit and generatesdata carrier, and in response the mobile unit answers the ringing andgenerates data carrier as described previously. The registrationcomputer 107 detects mobile generated data carrier (at 1501) and sends,for example, message #6 (registration telephone number 1) with thedigits of the telephone number used as registration telephone number 1when registering with the registration computer (at 1503). The receiptof this message at the mobile unit causes the mobile unit to store thedigits of the telephone number in the microprocessor 401 EEPROM storagelocation reserved for registration telephone number 1 (at 1505). Themobile unit then acknowledges the receipt of the message (at 1507). Theregistration computer, after receipt of the acknowledgment, may proceedin sending other information for programming the microprocessor 401EEPROM or it may terminate the call (at 1509) as previously described.The other messages shown in FIGS. 15A and 15B are the telephone numberto be stored in the mobile unit as registration telephone number 2 (at1511), the telephone number to be stored as the 611 assistance number(at 1513), and the individual bits which program the lock options andtiming of the mobile unit (at 1515). of course, it is possible toremotely program any of the numbers and options held in microprocessor401 EEPROM as illustrated in FIGS. 15A and 15B. The message may beconcatenated in a string as shown or they may be sent one at a time withother messages interspersed.

The status of any of the stored numbers or options may be queried asshown in FIG. 16. The call is made from the registration computer 107and acknowledged by the mobile unit as previously described. Afterdetection of the data carrier from the mobile unit (at 1601), amessage--for example message #5--is transmitted from the registrationcomputer (at 1603) to the mobile unit. Included with the message #5 is adata byte of 14. The mobile unit responds to the reception of themessage by reviewing the contents of the memory locations correspondingto the lock options (which is the meaning of data byte 14) and sendingthe lock option status, phone enable/disable status, and time out locktime to the registration computer (at 1605). The status of other optionsmay be requested serially or interspersed with other data. As shown, amessage #5 with a data byte 6 causes the mobile unit to respond with thecontents of the memory location corresponding to the registrationtelephone number 1 (at 1607, 1609) and a message #5 with data byte 9causes the mobile unit to respond with the stored credit card table (at1611,1613). When the requested status is complete, a terminate message#4 is transmitted to the mobile unit (at 1615) and both the mobile unitand the registration computer hang up.

In summary, then, the method and apparatus for communicating credit cardinformation for payment of mobile radiotelephone calls has been shownand described. A credit card magnetic stripe is read and a data field iscreated containing information such as the credit card identificationnumber. This data field is then formatted into a variable length datatransmission format which has cyclic redundancy and longitudinalredundancy suitable for protection of the data field againsttransmission errors introduced during radio transmission. Therefore,while a particular embodiment of the invention has been shown anddescribed, it should be understood that the invention is not limitedthereto since modifications unrelated to the true spirit and scope ofthe invention may be made by those skilled in the art. It is thereforecontemplated to cover the present invention and any and all suchmodifications by the claims of the present invention.

We claim:
 1. A method for communicating credit card information from amobile radiotelephone unit to a radiotelephone system in which aradiotelephone call from the mobile unit will be authorized if the costsof the radiotelephone call may be charged against a valid credit card,comprising the steps of:reading a credit card identification number andcreating a data field therefrom at the mobile unit; generating a messagehaving a format comprising:(a) an opening flag of at least onestart-of-header (SOH) character, (b) a data length character, (c) amessage type character, (d) said created data field, (e) at least onecyclic redundancy code character, and (f) at least one longitudinalredundancy check character; and transmitting said generated message froma transmitter of the mobile unit.
 2. A method in accordance with themethod of claim 1 further comprising the step of retransmitting saidgenerated message in response to a negative acknowledge signal beingreceived at a receiver of the mobile unit.
 3. A method in accordancewith the method of claim 1 wherein said step of reading a credit cardidentification number further comprises the step of reading a creditcard expiration date.
 4. A method in accordance with the method of claim1 wherein said at least one cyclic redundancy code character of saidgenerated message is further generated from said data length character,said message type character, and said created data field.
 5. A method inaccordance with the method of claim 1 wherein said at least onelongitudinal redundancy check character of said generated message isfurther generated from said data length character, said message typecharacter, said created data field, and said at least one cyclicredundancy code character.
 6. The apparatus for communicating creditcard information from a mobile radiotelephone unit to a radiotelephonesystem in which a radiotelephone call from the mobile unit will beauthorized if the costs of the radiotelephone call may be chargedagainst a valid credit card, comprising:means for reading a credit cardidentification number and creating a data field therefrom at the mobileunit; means for generating a message having a format comprising:(a) anopening flag of at least one start-of-header (SOH) character, (b) a datalength character, (c) a message type character, (d) said created datafield, (e) at least one cyclic redundancy code character, and (f) atleast one longitudinal redundancy check character; and means fortransmitting said generated message from the mobile unit.
 7. Theapparatus for communicating credit card information in accordance withclaim 6 further comprising means for retransmitting said generatedmessage in response to a negative acknowledge signal being received at areceiver of the mobile unit.
 8. The apparatus for communicating creditcard information in accordance with claim 6 wherein said means forreading a credit card identification number further comprises means forreading a credit card expiration date.
 9. The apparatus forcommunicating credit card information in accordance with claim 6 furthercomprising means for generating said at least one cyclic redundancy codecharacter of said generated message from said data length character,said message type character, and said created data field.
 10. Theapparatus for communicating credit card information in accordance withclaim 6 further comprising means for generating said at least onelongitudinal redundancy check character of said generated message fromsaid data length character, said message type character, said createddata field, and said at least one cyclic redundancy code character. 11.A method for communicating credit card information via a radiotelephonesystem having a plurality of mobile units with radio transceivers, atleast one base site transceiver, and a registration computer in which aradiotelephone call from a requesting mobile unit will be authorized ifthe costs of the radiotelephone call may be charged against a validcredit card, comprising the steps of:reading a credit cardidentification number and creating a data field therefrom at one of themobile units; generating a message having a format comprising:(a) anopening flag of at least one start-of-header (SOH) character, (b) a datalength character, (c) a message type character, (d) said created datafield, (e) at least one cyclic redundancy code character, and (f) atleast one longitudinal redundancy check character; transmitting saidgenerated message from a transmitter of said one of the mobile units;receiving said transmitted generated message at a receiver of said atleast one base site transceiver; calculating at least one local cyclicredundancy code character and at least one local longitudinal redundancycheck character at the registration computer; comparing said calculatedlocal cyclic redundancy code character to said at least one generatedmessage cyclic redundancy code character and comparing said at least onecalculated local longitudinal redundancy check character to said atleast one generated message longitudinal redundancy check character;transmitting an acknowledge signal from a transmitter of said at leastone base site transceiver if said comparison of said cyclic redundancycode characters indicates a substantial identity of characters and ifsaid comparison of said longitudinal redundancy check charactersindicates a substantial identity of characters; transmitting a negativeacknowledge signal from a transmitter of said at least one base sitetransceiver if said comparison of said cyclic redundancy code charactersand said longitudinal redundancy check characters indicates a mismatchof either character; and retransmitting said generated message, inresponse to said negative acknowledge signal being received at areceiver of said one of the mobile units.
 12. A method in accordancewith the method of claim 11 wherein said step of reading a credit cardidentification number further comprises the step of reading a creditcard expiration date.
 13. A method in accordance with the method ofclaim 11 wherein said at least one cyclic redundancy code character ofsaid generated message is further generated from said data lengthcharacter, said message type character, and said created data field. 14.A method in accordance with the method of claim 11 wherein said at leastone longitudinal redundancy check character of said generated message isfurther generated from said data length character, said message typecharacter, said created data field, and said at least one cyclicredundancy code character.
 15. A method in accordance with the method ofclaim 11 further comprising the steps of:receiving said acknowledgesignal at said one of the mobile units; timing the time after saidtransmission of said generated message from said one of the mobileunits; and retransmitting said generated message if said acknowledgesignal is not received within a predetermined time measured by saidtiming step.
 16. The apparatus for communicating credit card informationvia a radiotelephone system having a plurality of mobile units withradio transceivers, at least one base site transceiver, and aregistration computer in which a radiotelephone call from a requestingmobile unit will be authorized if the costs of the radiotelephone callmay be charged against a valid credit card, comprising:means for readinga credit card identification number and creating a data field therefromat one of the mobile units; means for generating a message having aformat comprising:(a) an opening flag of at least one SOH character, (b)a data length character, (c) a message type character, (d) said createddata field, (e) at least one cyclic redundancy code character, and (f)at least one longitudinal redundancy check character; means fortransmitting said generated message from said one of the mobile units;means for receiving said transmitted generated message at said at leastone base site transceiver; means for calculating at least one localcyclic redundancy code character and at least one local longitudinalredundancy check character at the registration computer; means forcomparing said calculated local cyclic redundancy code character to saidat least one generated message cyclic redundancy code character andcomparing said at least one calculated local longitudinal redundancycheck character to said at least one generated message longitudinalredundancy check character; means for transmitting an acknowledge signalfrom said at least one base site transceiver if said comparison of saidcyclic redundancy code characters indicates a substantial identity ofcharacters and if said comparison of said longitudinal redundancy checkcharacters indicates a substantial identity of characters; means fortransmitting a negative acknowledge signal from said at least one basesite transceiver if said comparison of said cyclic redundancy codecharacters and said longitudinal redundancy check characters indicates amismatch of either character; and means for retransmitting saidgenerated message, in response to said negative acknowledge signal beingreceived at a receiver of said one of the mobile units.
 17. Theapparatus for communicating credit card information in accordance withclaim 16 wherein said means for reading a credit card identificationnumber further comprises means for reading a credit card expirationdate.
 18. The apparatus for communicating credit card information inaccordance with claim 16 further comprising means for generating said atleast one cyclic redundancy code character of said generated messagefrom said data length character, said message type character, and saidcreated data field.
 19. The apparatus for communicating credit cardinformation in accordance with claim 16 further comprising means forgenerating said at least one longitudinal redundancy check character ofsaid generated message from said data length character, said messagetype character, said created data field, and said at least one cyclicredundancy code character.
 20. The apparatus for communicating creditcard information in accordance with claim 16 further comprising:means atsaid one of the mobile units for receiving said acknowledge signal;means for timing the time after said transmission of said generatedmessage from said one of the mobile units; and means for retransmittingsaid generated message if said acknowledge signal is not received withina predetermined time measured by said means for timing.